In sanitary wares such as toilet bowls or wash bowls, a glaze layer is provided on the outermost surface thereof from the viewpoints of ensuring a sanitary surface that is less likely to be contaminated and of ensuring design of appearance. The property that contaminants are less likely to be deposited can allow users to feel comfortable and, at the same time, can reduce a load on cleaning work of users. Because of this, various proposals have been made on sanitary wares having a surface that is less likely to be contaminated. For example, in order to improve antifouling properties by rendering the surface more smooth, JP 3339640B (PTL 1) proposes a technique in which Ra of the surface of sanitary wares is brought to 0.07 μm or less, and JP 4395821B (PTL 2) proposes a technique in which the surface is brought to such a state that silica particles having a particle diameter of 10 μm or more are absent.
In order to impart good design while having smoothness and antifouling properties, the surface of sanitary wares has a function of concealing the color of the sanitary ware body. An example of a method for concealing the color of the sanitary ware body is to add an opacifier such as zircon to glazes.
On the other hand, some of the present inventors have proposed in JP 2003-246647A (PTL 3) and JP 2003-246689A (PTL 4) sanitary wares produced using phase-separated glass. These publications disclose a method for forming a glaze layer having a two-layer structure on a sanitary ware by one film formation step. The claimed advantage is to impart functions such as strength and coloring to an underlying layer by adopting a construction of mutually different upper layer and lower layer. In particular, JP 2003-246647A (PTL 3) describes that the diameter of spherical particles is brought to 100 nm. According to this technique, a separated-phase structure of such spherical particles is previously formed and ground, and the spherical structure is melted to obtain a glaze layer. That is, in the techniques in these patent documents, glaze materials should be previously subjected to phase separation, and, further, there is room for an improvement in concealment of the body. In JP 2003-246647A (PTL 3), white color is developed due to crystalline nature to conceal the body. Accordingly, there is room for an improvement in alkali resistance.